Avoiding Chert as an Aggregate in Concrete

Which of the following is not considered an aggregate in concrete and should be avoided?

1) Gravels
2) Natural sand
3) Crushed stone
4) Chert

Final answer:

Chert is the material to be avoided as an aggregate in concrete due to its property of fracturing through grains, which can compromise the structural integrity of the concrete. Suitable aggregates include gravels, natural sand, and crushed stone, which enhance the durability and properties of concrete.

Explanation:

Among the options provided, chert is the material that is not considered an ideal aggregate for concrete and should be avoided. Chert is a type of sedimentary rock, composed mostly of microcrystalline quartz that is very hard and may have a smooth texture. One of chert's characteristics is that it tends to fracture through grains rather than around them, which can lead to weakened concrete structures. Unlike suitable aggregates like gravels, natural sand, and crushed stone, which are commonly used in the production of concrete for their desirable properties, chert can negatively affect the durability and structural integrity of concrete.

Concrete mixtures often include a blend of coarse and fine aggregates such as shale, clay, or slate, providing improved qualities for construction such as reduced load for faster building rates, extended longevity, and better thermal protection in comparison to brick. However, it's important to ensure that the aggregates chosen do not have adverse properties that could compromise the concrete's performance.